How do I apply all of my downloaded .tga textures to my model?
I am familiar with this scenario; it is common to have several texture maps assigned to a single model, especially in video games. You will need to know what geometry belongs to which texture, select that geometry, and then import and/or select the texture file in the UV Image Editor.

For example, the eye ball texture probably only belongs on the geometry that makes the eyes. So in edit mode, select only the eye geometry, and then in the UV editor you can select the appropriate texture. You can use things like the 'L' shortcut (select linked) to select connected geometry easily.